The present invention relates to a process and a device for treating seeds to combat seed- and/or soil-borne harmful organisms. The process and the device according to the present invention are intended for the treatment of agricultural, horticultural or forestry seeds, in particular, for the treatment of grain. The present invention is especially suited for combating smut in wheat or barley in agricultural production.
With specific cultivated varieties of grain, it is known that the seeds are dressed against seed-borne fungal pathogens. A plurality of chemical and physical treatment methods are known for this purpose. As a rule, the chemical treatment is carried out with dressing agents that contain one or several active substances. However, the specific pathogens of wheat smut (Ustilago tritici) and barley smut (Ustilago nuda) as well as other seed-borne harmful organisms can only be combated effectively by means of combined preparations which normally consist of a mercury compound and, a systemically attacking agent or of mercury-free combined preparations and at least one systemically attacking agent.
It is known in this connection that highly toxic chemicals are used. These have a wide range of action and are based on mercury compounds and their area of attack is the surface and seed shell of the seed corn. The mercury-free dressing agents which have either a small or a wide range of action make it possible to combat harmful organisms colonizing the deep regions of the seed corn. Furthermore, one expects of the above-described dressing operation with chemicals that these also protect the seed corn against soil-borne harmful organisms by adhering to the seed corn. Apart from a high deposition rate, the application of these agents requires specific devices which satisfy the conditions of application.
The disadvantages inherent to chemical dressing reside in the toxicity of the employed agents for warm-blooded animals and man and in developing resistance phenomena that can be observed during prolonged use with respect to specific harmful organisms. on the other hand, mercury-free dressing agents are much more expensive. Resistance also increases due to the fact that the standard treating agents (pesticides) contain the same active substances or active substances of the same groups as the dressing agents. Another aspect of the chemical dressing agents regards the residues thereof in cultivated plants and the associated negative effects on human and animal organisms. The amounts needed as well as metabolic phenomena are here of great importance. Finally, the known methods and devices for the chemical dressing of seeds have often the disadvantage that the fungicidal potency of the dressing agents is not fully exploited and that there is a potential risk of phytotoxic damage to the seeds caused by overdosage. The latter is often due to the uneven deposition of the dressing agent on the seed corns.
It is also known that the dressing agent is applied to the seeds in vacuum (DD-PS 18 675, DD-PS 23 421). The vacuum simultaneously serves to combat grain smut in an improved way through the additional action of moist heat. Devices of this type have however not gained any great importance because the procedure is very time-consuming and only a relatively small throughput can be achieved. Such a throughput does not meet the requirements of an efficient technological procedure, in particular in central seed processing installations.
Hot-water dressing has become known as a physical dressing method for combating barley smut. Although this method is very acceptable from an ecological point of view, as it is non-toxic and no harmful residues are left, it is not very successful and has thus not proved to be very efficient in practice.
The use of ionized high-energy rays, such as gamma or X-rays, to combat microbial harmful organisms on seeds is not possible because the necessary radiation dose would have mutagenic or phytotoxic effects on the seeds.
Furthermore, it is known that low energy electron beams are used in vacuum or in a free atmosphere to combat seed-borne harmful organisms (DD-PS 242 337, DD-PS 238 715, U.S. Pat. No. 4,633, 611). The electron energy and the radiation dose are chosen such that microbial harmful organisms are killed on the surface or in the near surface layers of the seed corn (caryopsis) without any produce affecting action or phytotoxic effects on the germ.
Although such a method has the advantage that it does not create any toxic effects and does thus not present any danger to man or his environment, seed-transferrable harmful organisms are not or only partly combated in the deep layers of the corn and in the germ, respectively, and the seeds are exposed to the attack of soil-borne harmful organisms in an unchecked way. Therefore, when barley or wheat smut causing agents are combated, electron dressing is not efficient enough because these agents colonize the deep layers of the caryopsis.
Biological combating methods which employ microbial antagonists that are used against seed-borne harmful organisms are now described more and more often (AT-PS 360 274, DE-OS 33 11 071, EP-PS 255 774, U.S. Pat. No. 4 798 723, etc.).
Bacterial antagonists, such as Bacillus spp., Streptomyces spp., Pseudomonas spp. and fungal antagonists, such as Chaetomium spp., Gliocladium spp., Penecillium spp., Trichoderma spp. and others are used. However, the good fungicidal effects found under laboratory conditions at optimum temperatures of more than 20xc2x0 C. are often not confirmed by outdoor tests, and there is considerable uncertainty about the effects thereof. To improve their efficiency, mixtures of microbial antagonists and fungicides were therefore used (see DE-OS 23 52 403, DE-OS 27 40 052, DD-PS 267 420).
At the present stage of the fight against harmful organisms by means of antagonists, it is regarded as a deficiency that the vitality and thus efficiency of these antagonists are limited by existing seed-borne harmful organisms, added fungicides with a wide range of action or unfavorable colonization conditions for the antagonists on the seed corn.
Finally, methods for the seed treatment with symbiotic microorganisms or mycorrhiza fungi have been suggested. It is the target of these measures to transfer microorganisms into the soil together with the seed corn. These microorganisms live in symbiosis with the useful plant or in the immediate vicinity thereof in the soil and provide important macronutrients for the useful plant through their metabolic products.
In this case, too, it might happen that above all seed-borne harmful organisms or fungicides with a wide range of action affect the development and thus efficiency of these microorganisms.
It is therefore the object of the present invention to provide a process of the above-mentioned type which is more effective in combating seed- and/or soil-borne harmful organisms and less harmful to the environment and permits a high throughput. Moreover, the process is meant to combat the harmful organisms on the seeds more efficiently, i.e. independently of the localization of the population of harmful organisms on the seed corn.
Furthermore, it is the object of the present invention to provide a device for treating seeds to combat seed-borne and/or soil-borne harmful organisms, with the device permitting a high throughput during the treatment of the seeds as well as a highly efficient treatment on all sides thereof in the combat against harmful organisms, i.e. independently of the localization of said organisms on or in the seeds.
As for the seed treating process, this object is attained according to the invention in that the seeds are subjected in immediate sequential order to a combined treatment with low energy electron beams and, thereafter, with active chemical substances and/or biological material.
Surprisingly enough it has been found that when the seed treatment to combat harmful organisms is carried out in two steps immediately following each other, namely the irradiation of the seeds with low energy electrons on all sides thereof in a first step and the immediately following treatment of the seeds irradiated in this way with an application of active chemical substances and/or biological material in a second step, this has a synergistic effect and produces an unexpectedly good result when seed- and/or soil-borne harmful organisms are combated. This surprisingly good effect of the process according to the present invention is explained by the fact that the low energy electron beams first help to combat the fungal harmful organisms on the surface and in the near surface region of the seeds or seed corns. Harmful organisms that have not been killed are sensitized in said regions and can more effectively be combated due to this sensitization immediately after electron dressing with active chemical substances and/or with biological material (especially microbial antagonists). When active chemical substances are used, it is possible to achieve a higher combating rate even if the amounts used are smaller. Since the sensitivity accomplished through electron dressing will not last forever, the procedure of treating the seeds in accordance with the invention in a continuous treatment process divided into immediately subsequent steps produces especially good results when harmful organisms are combated. Moreover, an improved deposition of the chemical and/or biological application and an improved depth action for chemical agents or microbial antagonists are achieved through the inventive process. The penetration depth can additionally be controlled through the selection of the pressure stage for the application of the active chemical substances and/or the biological material.
In a preferred embodiment of the present invention, the seeds are separated in a first step and moved through an irradiation chamber in a free-fall process and in vacuum, i.e. substantially evenly distributed in spaced-apart relationship, and are subjected, immediately thereafter in a second step, to an application with fungicides or the active substances and/or microbial antagonists thereof or the metabolic products and spores thereof and/or microorganisms (synergists) conducive to plant growth, possibly in conjunction with nutrients.
The seeds are preferably irradiated in the first step in a free-fall process in the irradiation region with quasi-monoenergetic electron beams on all sides, electrons of substantially reduced energy (scatter electrons) and plasma particles which act on the surface of the seed and a near surface layer outside the embryo.
In another preferred embodiment of the process of the invention the chemical and/or biological application of the second step is preferably carried out in vacuum, during the reduction of the vacuum after electron beam treatment of the seeds or under atmospheric pressure.
In case the treatment of the seeds is carried out after electron dressing in vacuum, a vacuum pressure is preferably chosen which corresponds approximately to the saturation vapour pressure of the application.
Other preferred embodiments of the process of the invention are shown in the remaining subclaims.
To attain the above-mentioned object with respect to the device for treating seeds to combat seed-borne and/or soil-borne harmful organisms, in particular to perform the above-explained process, the invention suggests a device which comprises an evacuated irradiation chamber into which the seeds can be introduced separately in a seed flow and through which the seeds are moved in a free-fall process, as well as electron beam generators for treating the seeds by spreading the electron beams in an irradiation region of the irradiation chamber, and at least one treatment chamber in flow communication with the irradiation chamber, connected to application devices for the chemical and/or biological treatment of the seeds.
The device preferably comprises an evacuated irradiation chamber with electron guns arranged thereon as well as feeders for the pressure-decoupled introduction and discharge of the seeds into and from the treatment chamber, furthermore a distribution device at an inlet point for the seeds into the irradiation chamber for separating the seeds, a fall shaft between the distribution means and an irradiation region of the irradiation chamber with at least two electron guns that are opposite to each other at the same level and with deflection devices which are used for spreading the electron beam and are assigned to the irradiation region, a treatment container, in particular a vacuum container, being in flow communication with the irradiation chamber downstream thereof via an intermediate feeder and comprising application devices for treating the seeds, which devices are preferably arranged inside the treatment container, and a supply vessel which is used for applying active chemical substances and/or biological material as well as microbial antagonists and is connected to the treatment container.
Other preferred embodiments of the device of the invention are outlined in the remaining subclaims.
Both with regard to the treatment of seeds with active fungicidal substances or agents and the treatment with antagonistic microorganisms and/or their nutrient broths, culture filtrates and antibiotic metabolic products following an irradiation of the seeds with low energy electrons, a surprising synergistic and increased effect was observed with respect to seed- and/or soil-borne harmful organisms without any produce-affecting phytotoxic effects. The low energy electron beam treatment in vacuum results in an advantageous predisposition to an essentially improved colonization of the seeds with used microorganisms or a permanent deposition of culture filtrates or antibiotic metabolic products on the seeds.